For years, many types of display devices have essentially been used in a binary mode, capable of providing only two density levels at each pixel location. These technologies were combined with various forms of bi-tonal halftoning to provide a simulated continuous tone reproduction capability. In bi-tonal halftoning, the appearance of intermediate shades of gray are created by a spatial modulation of black and white.
Recent improvements and advances in display technology have resulted in the availability of display devices with the capability of providing more than two levels of density at each pixel location. A variety of halftone algorithms have been developed which utilize the additional levels. This practice, known as multi-level halftoning, creates the appearance of intermediate tones by the spatial modulation of more than two tones, i.e., black, white, and one or more shades of gray.
In the existing art, U.S. Pat. No. 4,547,811 addresses multi-level halftoning techniques. The '811 patent relates to a method and apparatus for gray level processing, wherein images with less gray levels and many gray levels are reproduced in high quality. Additionally, U.S. Pat. No. 4,792,979 to Nomura et al relates to a method and apparatus for correcting the gradation of an image represented by image data. Although the prior art addresses the problem of density levels, i.e., minimizing system artifacts such as contouring and noise, the existing art does not address unstable display devices.
It is seen then that it would be desirable to have a process for optimizing an unstable output device.